1. Field of the Invention
The present invention generally relates to object transport and sorting systems and, more particularly, to object placement and stacking structures at destination pockets of such systems.
2. Description of the Prior Art
The transport of material and objects is an important feature of many industrial activities, particularly when material or objects must be moved on a large scale. Many such systems include arrangements for sorting of objects or material in accordance with properties thereof or indicia placed on the objects. For example, large volumes of mail or packages which must be transported to different locations must first be sorted in accordance with addresses placed thereon in the course of being transported to different locations in a sorting facility. Similar systems and applications may be encountered in baggage handling in airports and the like.
Such sorting of objects requires the objects to be handled in sequence in order to provide selectivity of handling and direction to various locations from which groups of objects that can be commonly transported to another location. This requirement generally implies that the objects must be transported at relatively high speed in order to accommodate the volume of objects which are presented. While it is possible to regulate the speed of objects somewhat in a high volume sorting apparatus, it is not generally possible to provide space to allow significant deceleration of objects as they approach their final destination in the sorting machinery. Therefore, as the object approaches a final destination such as a sorting bin or a stacker apparatus (sometimes referred to as a destination pocket or, simply, pocket) in the sorting system, the deceleration must usually be quite abrupt and often involves allowing the object to impact more or less violently on a surface or barrier such as the side of a destination pocket in a largely uncontrolled motion possibly including substantial rebound and, at least, not allowing the deposited articles to be placed in the destination pocket in an orderly fashion such as a stack.
Orderly positioning of objects in a destination pocket, often referred to as “neatness”, “raggedness” (e.g. “left-edge raggedness”) of, more generally, “stack quality”, is essential to avoid jamming of the system and damage to the objects following collisions between the trailing edge of an object and the leading edge of another object sent to the same bin, often in very rapid succession (e.g. as much as fifteen objects per second). Less than optimal stack quality and objects that assume a tilted orientation, in particular, present edges and surfaces and otherwise occupy a portion of the volume of the pocket where collisions are likely. Further, since these variations from an ideal stack are essentially random, they are not readily resolved by machinery once they occur.
For example, to improve the orderly placement of objects in a destination pocket, several additional types of device have been employed: one being of an auger type and another being a pneumatically actuated pusher. An exemplary mechanism including both of these known devices is shown in FIG. 5. (The depiction of FIG. 5 is arranged to illustrate operation of the known devices in a manner to facilitate comparison with the present invention and no portion of FIG. 5 is admitted to be prior art in regard thereto. Therefore, FIG. 5 has been designated as “Related Art”.) An incoming article or piece of mail is directed along plate 510 and one edge of the article is engaged by auger 520 which seeks to turn the article along the angled portion of plate 510. Once the article is turned, it may be pushed into place in a stack by pusher plate 530, actuated by pneumatic actuator 540. Sorting of mail pieces is accomplished by gates 550 which direct articles to one side or the other of roller 560 as they are passed along a path defined by rollers 570. It should also be appreciated that FIG. 5 illustrates a portion of the sorting mechanism which forms a part of the immediately downstream sorting mechanism and pocket.
Unfortunately, it has been found that collisions remain likely to occur between the leading edge of an object and some structure of the auger 520 or pusher 530, 540 as it manipulates objects previously placed in the pocket while continuing to allow rebound of a substantial number of objects which reduces the effectiveness of the additional structures and continues to be a source of collisions and jamming.
It has also been found that some widely used types of mail envelopes, particularly a back-side vertically oriented, end-flap-sealed C-5 envelope referred to as “Australia Post” which is of very light weight and flexible has proven very difficult to handle and is a major source of collisions, damage and jamming in mail sorting system including systems equipped with one of the additional auger or pusher device described above. In particular, as one envelope of the Australia Post type or an edge thereof is slid across another, an edge of one envelope will often engage an incompletely sealed portion of the sealing flap of another, preventing registration of envelopes in a stack or with the sides of the destination pocket. Further, it has been found, particularly in regard to the Australia Post envelope, that such auger and/or pusher devices are a source of article or object damage as well as a source of noise and particulates (e.g. cellulose paper dust) and a potential source of injury to personnel.
Since objects such as mail envelopes are often essentially “flown” into a destination pocket, and the importance of the aerodynamics of the objects has been recognized and, occasionally, exploited, it has been proposed to direct movement of objects with air currents. However, operational costs can become prohibitive when even moderate amounts of pressurized air at effective velocities are required. It is generally considered that the number of destination pockets required on many mail sorters would multiply such air requirements beyond the realm of feasibility even if relatively efficient arrangements could be designed. Further, any such arrangement must accommodate both incoming objects and objects previously deposited and exert control over such objects reliably over multiple degrees of freedom while the orientation and motion of the objects may vary widely to both establish and maintain good stack quality. In other words, the amount and number of features of control may be very limited consistent with other types of control which may be desired. Other factors which also present problems in the use of pressurized air are the generation of white noise and the generation of particulates which may affect the operation of the apparatus and possibly engender the potential for occupational hazards.